Who are these characters appearing during the talk about elder sister in Fate/kaleid episode 7?

Question

At around 13 minutes into episode 7 of Fate/kalied liner Prisma Illya 2wei!, when Illya's mother Irisviel talked about the power of an older sister, there are a few characters appearing in the background.

To quote Irisviel:

Older sister. Yes, that is the one who is older and has more power. When it comes to domestic hierarchies, they can hold more power than even the father. And they have absolute sway over younger siblings, which can never be overturned. The quote one great man, "No little sister is superior to her older sister!"

Who are these characters? And how does these characters compliements her argument about the power of an older sister?

Answer 1

They are character from the Nasuverse (which Fate/kalied liner Prisma Illya is set in).

From left to right

• Touko Aozaki - Kara no Kyokai, Mahou Tsukai no Yoru

  She is Aoko Aozaki's older sister, the one you see in the screen shot is how she looks in Mahou Tsukai no Yoru as she looks slightly different in Kara no Kyokai.

• Euryale and Stheno - Fate/Hollow Ataraxia

  They are the other 2 of the 3 Gorgon Sisters, as such they are related to Medusa, AKA Rider.

• Kohaku - Tsukihime

  One of the Heroines from Tsukihime and Hisui's sister who both serve as maids for the Tohno Household. Kohaku normally serves Akiha. However, her romantic interest is Shiki.

Irisviel's quote would refer to them all being the older siblings and having some sort of power over the younger siblings:

• Touko has a Sealing Designation and was seen as being the most powerful due to her superior Magic Circuits. However, her little sister Aoko was chosen to be the Aozaki Successor instead, which made Touko angry and caused the fight between the two (and thus the reason why Magus Families try to avoid sibling heirs). Touko was only defeated when Aoko used one of the 5 True Magics which was thought to be impossible. Otherwise, by specifications, she is still better that Aoko.

• Euryale and Stheno often picked on and belittled their younger sister Medusa and fed off her blood. However, they both did care very deeply for her. Chances are, if they were summoned as Servants, they would be more powerful than Medusa.

  After Medusa became the monster known as Gorgon, she devoured her sisters. However, when Perseus reflected the Nightmare of Breaker Gorgon back at Medusa, the "nightmare" Medusa saw was of the time she spent with her sisters, which made her paralyzed with joy of seeing them again, so they still hold power over her.

• Kohaku is a master at medicines and is often comically seen experimenting with them, (e.g. making a potion to turn Akiha into G-Akiha in Melty Blood), being a Magical Girl or making Mecha of Tsukihime Characters in her Underground Dungeon beneath the Tohno Household.

  In Tsukihime, she plots to get revenge on the Tohno Family due to her having been raped by Shiki's and Akiha's father as a child and later by SHIKI before releasing him (who then went to kill his father) because she (and her sister) are Synchronizers and resigned to this fate to protect her sister from suffering the same abuse.

The part about "[holding] more power than even the father" is strange, as none of them do we know the father of. If it's related, I assume it might refer to Kohaku as it was she who convinced Shiki's and Akiha's father to never touch Hisui when they were children and that it was because she was a Synchronizer who can keep him from giving into the Tohno Blood.